The present invention generally relates to machining materials, and more particularly, relates to a method and apparatus for forming openings in a workpiece with a broach and/or a hone. Although the present invention was developed for use in manufacturing gas turbine engine components, many applications may be outside this field.
It is well known that a gas turbine engine integrates a compressor and a turbine having components that rotate at high speeds thereby subjecting the components to significant centrifugal loading during operation of the engine. One component that rotates at high speeds is a disk that carries a plurality of blades that are designed to interact with the working fluid within the gas turbine engine. The plurality of blades is commonly attached to the disk through a blade attachment slot formed therein. Each of the blade attachment slots has a profile, which corresponds with the root of the blade, and has a configuration designed to retain the blade in the slot during operation of the engine. The blade attachment slots are generally of a xe2x80x9cfir-treexe2x80x9d configuration to increase the load bearing surface area of the disk, although other configurations are also utilized. Broaching is a technique often utilized for forming blade attachment slots in gas turbine engine disks. The relatively deep slotting generally associated with the formation of blade attachment slots in the disk is a relatively time consuming and costly operation. In a typical broaching process a broaching tool with a series of cutting teeth is pulled through a workpiece to remove material and form the desired opening. Each cutting tooth is typically slightly different from the adjacent cutting teeth, and the broach is designed to gradually remove material from the workpiece and create a blade attachment slot. Broaching tools have been used for many years and include: a unitary broach having a plurality of cutting teeth formed on a single solid broach bar; and an insertable broach including a tool body having a plurality of removable cutting inserts fixed thereto.
Typically, the blade attachment slots are formed in a three-stage broaching operation. The rough shape of the attachment slot is generally formed during an initial rough broaching stage. After the rough broaching stage, an intermediate broaching stage is used to form the intermediate shape of the slot. Finally, a finishing broaching stage is generally used to form the profile of the attachment slot. One limitation associated with many prior three-stage broaching operations is the time required on the broaching machine to form the plurality of blade attachment slots in the disk. Another limitation associated with many prior three-stage broaching operations is the resulting surfaces formed on the disk by the broaching process often have ripples formed thereon as a by-product of the broaching operation. The ripples on the blade attachment slot surfaces can lead to a decreased disk life because of fretting between the blade root and the disk surface during engine operation.
As will be described in detail below, the present invention provides a novel and unobvious method and apparatus for forming openings in a workpiece.
One form of the present invention contemplates a broach assembly, comprising: a plurality of broaching cutting inserts having a cutting surface; and, a main body member having a plurality of spaced compression mounts formed thereon and aligned in a row, each of the plurality of compression mounts has one of the plurality of cutting inserts positioned therein in an interference fit.
Another form of the present invention contemplates a broach assembly, comprising: a carrier body having a plurality of integral support members aligned in a row and spaced along the carrier body; a plurality of spacers aligned in the row and coupled to the carrier body, one of the plurality of spacers is located between an adjacent pair of the plurality of support members, the pair of the plurality of support members defines a first support member and a second support member, and the one of the plurality of spacers abutting the first support member; and, a cutting insert disposed between the second support member and the one of the plurality of spacers, the cutting insert is wedged between the one of the plurality of spacers and the second support member, and wherein the second support member braces a substantial length of the cutting insert during broaching.
Yet another form of the present invention contemplates a method for reworking a unitary broach bar having a plurality of cutting teeth integrally formed on a broach bar. The method, comprising: providing at least one broach assembly having a carrier with a plurality of cutting inserts; removing a section of the unitary bar including a plurality of cutting teeth; positioning the at least one broach assembly on the broach bar in place of the section after the removing; and, securing the at least one broach assembly to the broach bar with at least one coupling member.
Yet another form of the present invention contemplates a broach, comprising: a broach bar having a first portion including a plurality of integrally formed cutting teeth and a second receiver portion defining a section free of integrally formed cutting teeth; and, at least one broach assembly having a plurality of removebable cutting inserts mechanically coupled thereto, the at least one broach assembly coupled to the broach bar in the second receiver portion.
Still yet another form of the present invention contemplates a method for forming a blade attachment slot in a gas turbine engine disk. The method, comprising: broaching the disk to remove material and define a blade attachment slot of a predetermined profile; and running a substantially full form hone through the predetermined profile to flatten the surfaces of the disk after the broaching and produce a final blade attachment slot profile.
Still yet another form of the present invention contemplates a gas turbine engine disk, comprising: a metallic disk having a first surface and an opposite second surface and a perimeter, the disk has a plurality of spaced blade attachment slots machined therein between the first surface and the opposite second surface and located around the perimeter, and a plurality of surfaces defined on the disk that form the blade attachment slots are substantially smooth and flat after a substantially full form honing process.
One object of the present invention to provide a method and apparatus for forming an opening in a workpiece.
Related objects and advantages of the present invention will be apparent from the following description.